Parkinson's disease (PD), is the most common neurodegenerative movement disorder, and it^.shares many common features, such as protein aggregation, with a broader spectrum of neutodegenerative diseases. PD can present with additional clinical impairments and dementia is common in PD patients. Despite the knowledge that the loss of specific dopaminergic neurons in the midbrain is largely responsible for most of the motor dysfunction in PD, there are significant unknown about the mechanism that lead to neuronal death. Although familial PD is relatively rate, the identification of mutation in the alpha-synuclein gene has lead to the discovery that this protein is the major component of disease-characteristic inclusions known as Lewy bodies and Lewy neurites. Alpha-synuclein is normally a soluble protein, but it can polymerize into 10-15 nm fibrils with specific biophysical properties known as "amyloid" to form pathological inclusions. Pathological inclusions such as intracellular neurofibrillarytangles and extracellular Abeta peptide deposits, which are characteristic of Alzheimer's diseasae, frequently present concomitantly with alpha-synyuclein aggregates. Indeed, apha-synuclein and tau inclusions can occur in the same cells, often intertwined. Alpha-synuclein has been shown to be able to act as an induceer of tau aggregation, and both proteins can enhance the ploymerization of each other once this process is initiated. However, the molecular mechanism and the physiological changes that lead to this process have not been elucidated. Test tube experiments and transgenic mice studies will be conducted to address these issues. Studies will be conducted to assess selective vulnerability and behavioral impairments in transgenic mice resulting from alpha-synuclein and tau interactions leading to the formation of pathological consequences. Aberrant physiological alterations,such as nitrative damage and hyperphosphorylation, may be involved in mediating alpha-synuclein and tau interactions and these mechanisms will be investigated. Transgenic mouse models of Abeta peptide deposits will also be used to assess possible pathological mechanisms by which these inclusions may promote alpha-synuclein aggregation. These findings shown provide important information on mechanisms and physiological changes that lead to the formaion of alpha-synuclein and tau inclusions, and may lead to insights in planning for effective therapeutic approaches.